1. Field of the Invention
The present invention relates to chip electronic parts used in chip inductors, chip coils, chip capacitors, etc.
2. Description of the Related Art
Conventionally, the rectangular chip coil shown in FIG. 8 has been known in the art. This type of chip coil has the following structure: a coil pattern 2 and leading electrodes 3 are formed on a ceramic member 1; an insulating protective layer 4 covers the entire face of the coil pattern 2 and portions of the leading electrodes 3; external electrodes 5 electrically connected to the corresponding leading electrodes 3 are formed on the corresponding end faces of the ceramic member 1. Each of the external electrodes 5 is composed of: a Cr undercoating layer 5a formed by dry plating such as sputtering; and a Ni plating layer 5b and a solder plating layer 5c, both produced by wet electrolytic plating.
According to the above conventional chip coil, when the undercoating layers 5a are formed on the corresponding end faces of the ceramic member 1 by dry plating, e. g. sputtering, a sputtering material inevitably extends to the upper and lower faces of the ceramic member 1 and the plating layers 5b and 5c are formed thereon by electrolytic plating. In this case, the length of the upper extension E1 and that of the lower extension E2 are the same in each of the external electrodes 5. A certain length of the lower extension E2 is required to solder the external electrodes 5 to a print substrate. Thus, the length of the upper extension E1 is correspondingly increased to ensure a certain length of the lower extension E2.
However, an increase in the size of the upper extension E1 leads to a decrease in the effective area for forming a conductor pattern on the ceramic member, which fact is a great problem because small-sized electronic parts are in demand nowadays. Further, the size of the upper extension E1 alters according to the shape of the conductor pattern or the insulating protective layer, and the electrical characteristics thereby undesirably deteriorate or vary widely due to, e.g., inductive coupling between the pattern coil 2 and the upper extension E1 of the external electrode 5.
Conventional chip electronic parts are prepared as follows: A large-area ceramic base material is partitioned into portions by primary dividing grooves and secondary dividing grooves running in the transverse and longitudinal directions, respectively, and a conductor pattern and an insulating protective layer are formed in each portion according to a matrix pattern. After obtaining stick-shaped base material by primary-cutting the ceramic base material along the primary dividing grooves, the external electrodes are provided on the corresponding end faces, in which process a sputtering material of the undercoating layer enters into the secondary dividing grooves and plating layers are further formed thereon. As a result, the external electrodes are formed also in the secondary dividing grooves, and the electrical characteristics of the device thereby undesirably deteriorate or vary widely.